Our muscle tissue consists of fibers (cells) that are highly specialized for the active generation of force for our muscle contraction. Muscle tissue provides motion, maintenance of our posture, and heat production. On the basis of certain structural and functional characteristics, the muscle tissue that our body has is classified into three types: cardiac, smooth and skeletal.
Cardiac MuscleCardiac muscle tissue forms the bulk of the wall of the heart. Like skeletal muscle tissue, it is striated. Unlike skeletal muscle tissue its contraction is usually not under conscious control and is classed as involuntary.
Smooth MuscleSmooth muscle tissue is located in the walls of hollow structures such as blood vessels, the stomach, intestines, and the bladder. Smooth muscle fibers are usually involuntary, and they are non-striated (smooth). Smooth muscle tissue, like skeletal and cardiac muscle tissue, can undergo hypertrophy (growth).
Skeletal MuscleSkeletal muscle tissue is attached to our bones. It is striated; that is, the fibers (cells) contain alternating light and dark bands (striations) that are perpendicular to the long axes of the fibers. Skeletal muscle tissue can be made to contract or relax by conscious control (voluntary).
All skeletal muscle fibers are not alike in structure or function. For example, skeletal muscle fibers vary in colour depending on their content of Myoglobin (Myoglobin is found in muscle tissue, where it binds oxygen, helping to provide extra oxygen to release energy to power muscular contractions.) Skeletal muscle fibers contract with different velocities, depending on their ability to split Adenosine Triphosphate (ATP). Faster contracting fibers have greater ability to split ATP. In addition, skeletal muscle fibers vary with respect to the metabolic processes they use to generate ATP. They also differ in terms of the onset of fatigue. On the basis of various structural and functional characteristics, skeletal muscle fibers are classified into three types: Type I fibers, Type II B fibers and type II A fibers.
Type I FibersThese fibers, also called slow twitch or slow oxidative fibers, contain large amounts of Myoglobin, many mitochondria and many blood capillaries. Type I fibers are red, split ATP at a slow rate, have a slow contraction velocity, very resistant to fatigue and have a high capacity to generate ATP by oxidative metabolic processes. Such fibers are found in large numbers in the postural muscles of the neck.
Type II A FibersThese fibers, also called fast twitch or fast oxidative fibers, contain very large amounts of Myoglobin, very many mitochondria and very many blood capillaries. Type II A fibers are red, have a very high capacity for generating ATP by oxidative metabolic processes, split ATP at a very rapid rate, have a fast contraction velocity and are resistant to fatigue. Such fibers are infrequently found in humans.
Type II B FibersThese fibers, also called fast twitch or fast glycolytic fibers, contain a low content of Myoglobin, relatively few mitochondria, relatively few blood capillaries and large amounts glycogen. Type II B fibers are white, geared to generate ATP by anaerobic metabolic processes, not able to supply skeletal muscle fibers continuously with sufficient ATP, fatigue easily, split ATP at a fast rate and have a fast contraction velocity. Such fibers are found in large numbers in the muscles of the arms.